The present invention relates in general to active bolsters for occupant crash protection in automotive vehicles, and, more specifically, to an active bolster with an inflatable bladder formed by plastic wall panels that is vented to manage deflation during impact.
An active bolster is a vehicle occupant protection device with a gas-inflatable bladder to absorb impacts and reduce trauma to occupants during a crash. As opposed to deployable air bag cushions made of various fabrics that emerge from behind various openings upon inflation, active bolsters use the interior trim surface itself to expand at the beginning of a crash event for absorbing the impact and dissipating energy through the action of an inflation gas. U.S. Pat. No. 8,205,909, issued Jun. 26, 2012, incorporated herein by reference, discloses an active knee bolster integrated into a glove box door that is light weight and visually attractive. U.S. Pat. No. 8,474,868, issued Jul. 2, 2013, also incorporated herein by reference, discloses a typical structure wherein an active bolster includes a front wall or panel (i.e., a trim panel) that faces a vehicle occupant attached to a back wall or panel (i.e., bladder wall) along a sealed periphery. One or both of the walls is deformable in order to provide an inflatable bladder. For example, the back wall may have a pleated (i.e., accordion-like) region that straightens out during inflation. The walls are initially spaced apart by a small amount when in their pre-deployment, non-inflated condition. This allows ingress of the inflation gas in a manner that achieves an even inflation across the panel.
The front and back walls of a typical bladder for an active bolster are comprised of molded thermoplastics such as polyethylene, polyolefin, or PVC. They are typically injection molded but can also be blow molded. When formed separately, the front and back walls must be hermetically joined around their periphery in order to form the inflatable bladder. The joint must be strong to resist separation that could result from the high pressures during inflation. The peripheral seal is formed by hot welding, for example.
It is known that in order to optimize the dissipation of energy when an occupant contacts an air bag or an active bolster, inflation gas should be vented to allow a controlled collapse of the airbag that safely decelerates the impacting occupant. U.S. Pat. No. 8,328,233, issued Dec. 11, 2012, which is incorporated herein by reference, discloses a variable vent for an active bolster wherein the vent has a low flow rate at low pressures and a higher flow rate at higher pressures across the vent. The reduced flow rate of the vent during initial stages of inflation permits the use of a smaller (less costly) inflator, while the higher vent flow rate at higher pressures helps ensure the integrity of the peripheral weld by limiting the pressure rise and avoiding large tearing forces that could cause the seal to fail.
Various types of structures have been disclosed for venting an adaptive amount of inflation gas during inflation and during loading by an impacting passenger. For example, hinged flaps providing a small opening at low pressure and a larger opening at higher pressure have been formed in the back bladder wall. The size, placement, and desired performance characteristics for an active bladder are typically unique for each vehicle model that is developed by a vehicle manufacturer. Since the bladder wall may be redesigned for each new vehicle design, a significant development effort must be is devoted to finding an appropriate placement and configuration for one or more vent features according to the unique design specifications. It would be desirable to provide a venting structure that is usable across many different designs and that reliably provides an appropriate amount of venting (including no venting, i.e., a sealed condition) at the appropriate times.